Chlorofluorocarbons (CFC's) are useful in a wide variety of applications, such as refrigerants, propellants, solvents and the like. Many CFC solvents such as chlorofluoromethanes and chlorofluoroethanes are known to provide safe and reliable cleaners and are useful in numerous applications. For example, 1,1,2-trichlorotrifluoroethane is widely used as an agent for removing oil, grease and related contaminants from many plastic materials. That use, however, also poses the same environmental problems described above. Therefore, stabilization of these CFC cleaning solutions is also desirable.
CFC's are also used in conjunction with other materials in cleaning applications. For example, CFC-alcohol azeotropic cleaning solutions are all widely used in cleaning medical devices such as dialyzers. Dialyzers, or "artificial kidneys", function as superfine strainers, permitting passage of molecules only up to a certain size through semi-permeable membranes used therein. Dialyzers, in effect, perform the functions of the kidney in removing waste from the blood and regulating the body's internal environment.
One known dialyzer configuration is a capillary flow dialyzer, comprised of a plurality of hollow fibers contained within a housing. Such capillary flow dialyzers may be manufactured in any number of ways. In one process, the fibers are extruded using isopropyl myristate as a lubricant. Isopropyl myristate, while effective as a lubricant, tends to leave a residue on the fiber which must be cleaned prior to use. Other contaminants may also be generated or deposited on the fiber surfaces as a result of the manufacturing and assembly of such dialyzers. These contaminants too must be cleaned prior to use, because their presence could cause a reaction in patients ultimately using the device.
One known CFC-alcohol azeotropic cleaning solution is Freon/TP Azeotrope which includes about 97 weight percent Freon TF and about 3 weight percent isopropanol. (Freon is a registered trademark of the E. I. duPont de Nemours Co., Wilmington, Del., USA). Freon/TP Azeotrope is known to provide an efficient, high quality cleaning solution enabling both alcohol soluble residues and non-alcohol soluble residues to be cleaned from an article such as a dialyzer.
While beneficial as a cleaning solution, it is known that under certain circumstances, such as are present during the process of cleaning dialyzers, Freon TF (a component of Freon/TP Azeotrope) will react with the alcohol to release hydrochloric acid (HCl) or, alternatively, any evolved chloride will protonate in the environment to yield the acid. This production of hydrochloric acid (HCl) causes the pH in the cleaning system to drop to a pH generally below 4.5 to 7.0, the normal range for Freon azeotropes. In turn, stainless steel in the cleaning apparatus itself undergoes a conversion reaction in this chloride rich acidic environment. More particularly, after several hours of operation, the stainless steel, the water separators, and the water flush of the cleaning apparatus using Freon/TP may turn green. Such "green outs" are indicative of corrosion of the apparatus which can be so severe that it causes irreparable pitting. Additionally, these "green outs" can cause damage to the medical devices, e.g., dialyzers, being cleaned.
Hydrochloric acid (HCl) is likely produced due to a reaction between the major components of the azeotropic cleaning solution. Particularly, it is believed that the Freon TF (CF.sub.2 ClCFCl.sub.2) reacts with the isopropanol ((CH.sub.3).sub.2 CHOH) according to the following mechanism: ##STR1## The generation of hydrochloric acid according to this mechanism continues as long as the conditions permit, unless it is inhibited, neutralized or stabilized.
Known methods of stabilizing CFC compositions are disclosed in Japanese Patent No. 1,221,333 published Sep. 4, 1989 and U.S. Pat. No. 4,454,052 issued Jun. 12, 1984. These methods involve the use of epoxides which are disclosed as being useful for stabilizing the chlorofluorocarbon and inhibiting corrosion of metal. These compounds when reacted form highly toxic, possibly carcinogenic materials, rendering them unsuitable for use in cleaning medical devices, such as dialyzers.
Conventional stabilizers for chlorofluorocarbonalcohol azeotropes include nitromethane, 3-methyl-1-butyne-3-ol, glycidol, phenyl glycidyl ether, dimethoxymethane, hexene, cyclopentine, allyl alcohol, methacrylate, and butacrylate. See Japanese Patent No. 1,165,698 published Jun. 29, 1989. The toxicity and volatility of these compounds, like those mentioned above, render them unsuitable for cleaning medical devices of the type which can be cleaned in accordance with the present invention.
This invention addresses the corrosion problem known to occur through use of CFC cleaning compositions in certain environments. In particular, this invention provides a mechanism to effectively, safely and in a reproducible manner, scavenge the acid produced through the use of chlorofluorocarbon-alcohol azeotropic solutions in conventional cleaning applications. Operator inhalation of chlorine is reduced or eliminated.